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Flume Experiments to Determine the Erodibility of Gravel Streambank Soils

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan

Citation:  Paper number  131620973,  2013 Kansas City, Missouri, July 21 - July 24, 2013. (doi: @2013
Authors:   David T Criswell, Garey A Fox, Ron B Miller, Erin Daly, Abdul-Sahib Al-Madhhachi
Keywords:   Erodibility; Excess Shear Stress Model; Fluvial Resistance; Streambank Erosion; Wilson Model

Abstract. Fluvial erosion in streambank stability models is typically modeled using an excess shear stress equation based on two soil parameters: the erodibility coefficient (kd) and critical shear stress (τc). For cohesive soils, methods exist such as jet erosion tests (JETs) for measuring kd and τc. For noncohesive bank materials such as sands and gravels, τc is commonly estimated using the Shields diagram based on the median particle diameter. However, no universally accepted relationship exists for estimating kd for noncohesive soils. Also, recent research has proposed the use of more fundamentally-based mechanistic detachment models in place of the excess shear stress equation, but limited research has been performed in deriving the parameters of these alternative detachment models. One such model investigated in this research is the Wilson Model, which is based on two parameters: b0 and b1. The objectives of this research included the following: (i) conduct flume experiments on noncohesive gravels to quantify detachment rates relative to the imposed shear stress, (ii) derive kd and τc and b0 and b1 for these gravels, (iii) determine if relationships can be developed relating kd versus τc and b0 versus b1, (iv) compare the kdc relationship to previously proposed relationships, and (v) compare the relative performance of the models in being able to fit the scour data. Flume experiments were conducted at the USDA-ARS Hydraulics Laboratory. Samples of gravels were extracted from streambanks on the Barren Fork Creek in eastern Oklahoma. The samples were sieved into particle size classes and then at least triplicate flume experiments were performed with average gravel sizes of 0.45, 0.60, 1.30, and 1.90 cm (0.18, 0.25, 0.50, and 0.75 inches, respectively). Scour depth was measured using a point gage during the flume experiment. The kdc relationships derived from the laboratory experiments followed a power law relationship with the form: kd=2.23τc-0.50 (R2 = 0.65). The Wilson Model parameters b0 and b1 derived from this research appeared to have a similar relationship but different magnitude than kd and τc. The kdc or b0-b1 relationships can be used to model fluvial erosion of the noncohesive gravel and therefore the resulting streambank failure of composite banks.

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